132 NATURE STUDY 



Set up the experiment in accordance with their direc- 

 tions. 



If the children do not know that the water passes into 

 the air, write on the blackboard with a wet sponge, or 

 wring out and hang up to dry a piece of cloth, etc., and 

 let them watch the drying. 



Do clothes dry more rapidly in winter or in summer? 

 When the air is still or in a wind? 



Why did the water evaporate more quickly in the 

 shallow dish than in the deeper one ? How can we find 

 out certainly whether heat and wind hasten evaporation ? 



Set up the experiments in accordance with their direc- 

 tions. In these, as in all other experiments, the teacher 

 must see that the children eliminate all unequal condi- 

 tions. For example, the volumes of water in the two 

 dishes must be equal ; the remaining volumes must be 

 exactly measured; when experimenting with tempera- 

 ture both dishes must be protected from currents of 

 air, and vice versa. 



By means of a spirit lamp, or a Bunsen burner, Avater 

 may be made to boil in a kettle or dish with a spout 

 in the presence of the seated children. Lead them to 

 see that the steam is invisible near the spout, and that 

 a flame held below the steam beyond makes it invisible 

 again. 



Tell them to boil some water in a shallow dish on the 

 stove at home, and to bring you the answers to the fol- 

 lowing questions: What happens just before the water 

 begins to boil? Where do the bubbles form? Where 

 are they largest ? 



Send them all to the blackboard. Let them touch it 

 with their Angers. Is it warmer or colder ? Let them 

 breathe on it. What has happened ? Where did the 



